Rotation bugfix.

[atsar]

No description provided.

[runspired]

As this is a reversal of atsar@287720a I'd like more info on what the perceived bug is.

[atsar]

The getRotation function returns the change of the angle since the rotation start. When you land two fingers on the screen, it gives start[0] and start[1] points that determine the orientation relative to the screen. Then, when you move them, it gives end[0] and end[1] - new current finger locations. So, the rotation is the difference (minus) between the end orientation and the start orientation. If you put plus there, it simply gives incorrect number.
Imagine that you just start the rotation. Then end=start, and the rotation should be zero. Having plus in the formula gives you the doubled angle between the line connecting your fingers and the screen horizontal, which is meaningless.

[arschmitz]

@runspired the logic in this PR is correct let me explain.

the formula to get the angle relative to the screen for 2 points is
angle = atan2( y2 - y1, x2 - x1 ) * 180 / Math.PI

No lets take the very simple case of our starting points being at 1,1 and 3,1 using the formula above this gives us a starting angle of 0

No we move the second point to 3,3 this is a 45 degree rotation and this is confirmed using the formula above. Since we started at 0 and end at 45 45 - 0 = 45 so the total rotation is 45 which is also the result of the current formula 45 + 0 = 45 This is correct since we rotated in the positive direction.

This can also be confirmed in the negative or counterclockwise direction. Again starting at 1,1 and 3,1 this time we move the first point to 1,3 and leave the second one in place. The above formula gives us an angle of -45 then subtracting the 2 angles we get -45 - 0 = -45 which is correct since we rotated in the negative direction this time.

Where the current formula fails to work is in a non zero case. take starting points of 1,1 and and 3,3 and ending points of 1,1 and 1,3 the angles for these points is 45 and 90 respectively the current formula would give 90 + 45 = 135 which is clearly wrong since we only rotated 45 degrees in the positive direction. the new formula would yield 90 - 45 = 45 which is the correct result.

[arschmitz]

looking back at 287720a this is not a regression of #791 which it claims to fix but rather #791 was never fixed and this commit was just not correct.

[runspired]

I would like to get this merged @arschmitz I think it resolves the 90deg jump issue.

[arschmitz]

@runspired sounds good to me based on my comment above i think this is completely correct we just need to get the conflict resolved

[sebastianrothe]

whats the status on this merge ?

[bobrosoft]

@arschmitz hey there! Almost a year has passed. Can it be merged? Need it resolved.

[magicznyleszek]

@arschmitz is this project dead?

[laborc8]

I had big problems with the pinch and rotate example on the webiste. No solution really worked.
But this bugfix totally solved it.
So for everyone who is looking for a bugfix for the pinch and rotate problem (jumping the moment you touch aso...) use this bugfix - just change the + to a minus and it works

[squadette]

This has been applied in proposed 2.1.0: squadette#1

@arschmitz, thank you for the detailed explanation.

[asturur]

Any chance to merge this fix if we open a pr with conflict solved?